1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for electrically biasing a substrate in an electrochemical processing system.
2. Description of the Related Art
Electrochemical Mechanical Polishing (ECMP) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion compared to conventional Chemical Mechanical Polishing (CMP) processes. The electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. Typically, the bias is applied to the substrate surface by a conductive polishing pad on which the substrate is processed. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the conductive polishing pad which enhances the removal of the conductive material from the substrate.
During the ECMP process, conductive elements disposed in the conductive pad must maintain contact with the conductive layer of the substrate in order to achieve good processing results. If the conductive elements intermittently contact the conductive layer, the power source providing an electrical bias through the conductive elements may be damaged. Moreover, intermittent contact may result in current spikes as contact is made that may damage both the materials disposed on the substrate and the conductive elements themselves. Additionally, current spikes through the conductive elements may degrade the conductive properties at the surface of the conductive elements, thereby limiting and causing non-uniform current flow through the conductive element, resulting in unsatisfactory processing results.
To maintain good electrical contact between the conductive elements and the substrates, the conductive elements may be biased against the substrate by springs or electrolyte fluid flow. However, it is difficult to control the spring force applied to the conductive elements, and excessive spring force may lead to substrate scratching. Additionally, biasing the conductive elements using electrolyte flow may result in excessive quantities of electrolyte being utilized in order to achieve a desired bias force.
Thus, there is a need for an improved method and apparatus for electrically biasing a substrate in an electrochemical processing system.